Grid for fluidized solid vessels



Feb. 27, 1968 I s. A. GUERRIERI 3,370,361

GRID FOR FLUIDIZED SOLID VESSELS Filed April 27, 1965 y INVENTORSalvatore A. Guerrieri Z4 l BY mlm ATTORNEYS United States Patent O3,370,361 GRID FOR FLUIDIZED SOLID VESSELS Salvatore A. Guerrieri,Rowayton, Conn., assigner to The Lummus Company, New York, N.Y., acorporation of Delaware Filed Apr. 27, 1965, Ser. No. 451,297 8 Claims.(Cl. 34-57) ABSTRACT OF THE DISCLOSURE This invention relates to a noveldistributing grid for use in distributing one or more vapor streams toachieve effective fluidizing contact with a bed of particles. The gridof the present invention includes an upper cylinder portion having anoutwardly extended flange, and a lower generally conical perforatedportion, the upper cylindrical portion being smaller than the insidedimension of the reactor body in which the grid is mounted'so that thegrid is spaced inwardly therefrom.

In many industrial processes, it is desirable to contact solid particleswith a uid stream in a manner known as lluidizing the bed of particles.The particles are contacted by passing the gaseous fluid up through abed thereof, so that the bed of particles expands and the particles areout of continuous contact with each other and in a state of relativelyhigh mobility and density, thereby achieving good interfacial contactand uniform bed temperatures. An expanded bed of uidized particlesresembles a boiling liquid, with respect to appearance as well ashydrostatic and hydrodynamic properties, and has a mobile but distinctupper surface with small pockets of gas emitting therefrom. Fluidizedbeds promote good contact between gases and solids, reduce channellingproblems, bring about effective utilization of all particles and causeextremely even utilization of heat and materials. An example of one useof a uidized bed of particles is in the catalytic cracking of petroleumwherein a vapor phase petroleum fraction is contacted with a iluidizedbed of heterogeneous silica-alumina catalyst particles. Another exampleof the use of fluidized beds is in the carbonization and gasification ofshale oil fines. In the former instance the fluid medium is the reactantand the solid serves only as a catalyst but in the latter instance, thesolid is itself a first reactant and the fluidizing medium, steam andair, is a second.

To obtain proper uidization of the solid particles, it is necessary todistribute the iiuid evenly through the lower portion of the bed so thatno large bubbles of uid pass through the bed, and so that no portion ofthe bed offers more resistance to uid iiow than any other portion of thebed. lt is also necessary to construct a distributor or grid which hassufficient structural strength to support the entire bed of solid in theunfluidized condition in case of shutdown, an upset or accidental lossof gas pressure which causes the fiuidized bed to collapse.

In order to increase structural strength, use of a distribution gridwhich is dome shaped has been suggested, since at grids tend to bend orbuckle under the weight of the bed in the unfluidized condition. Thedome-shaped grid, however, is higher in the center than at the edges, sothat less head of iluidized bed is above the central portion of the gridwhich, therefore, causes less resistance to ow at that point. As aresult, a greater portion of the fluid flows to the center of the bedthan to the periphery, and proper uidization of particles is notobtained.

In many applications a flat grid cannot be supported around its edges bythe vessel walls, since the metal-to metal contact of the grid with thevessel Wall causes heat conduction through the grid to the wall, withthe result that a weakened hot spot on the vessel wall is created. Thehot grid and cold metal wall also cause strains due to differentialexpansion that tend to buckle either the grid or the vessel. Thedistribution grid within the vessel must, therefore, be oating so thatit may expand and contract without straining the vessel wall and so thatit does not conduct heat through the insulation to the vessel wall. Ofcourse, these limitations apply equally to at or shaped distributiongrids, in that any contact with the vessel walls provides a heat sinkwhich will conceivably have adverse effects.

In order to obtain satisfactory distribution of the uid stream, it isnecessary that there be a substantial pressure drop in the stream as itpasses through the grid. If this is done, each perforation in the gridwill pass the same amount of uid per unit area; in this regard it isadvantageous to pass the iluid into a single chamber directly below thegrid and introduce it therefrom through the perforations and thence intothe uidized bed.. 0f course, such a chamber, in which a higher pressureis maintained, tends to push the distribution grid upwardly, and a largeflat plate, forming the top closure of the chamber, will tend to buckleoutward. Thus, it may be seen that distribution grids in fluidized bedassemblies are subject to stresses and strains in both directions; theytend to buckle downward under shutdown conditions when the bed collapsesonto the grid, and they tend to buckle upward, into the chamber, if gaspressure below the grid becomes too great.

In addition to the upward and downward forces which the distributingplate must sustain, provision must also be made for the thermalexpansion and contraction of the distributing plate, inasmuch as it issubjected to much higher thermal cycling than the reactor shell.

It is therefore a general object of the present invention to provide animproved distribution head for use in a uidized bed reactor which issimple and economical to construct, which provides an improvediluidizing action within the bed, and which readily sustains the variousthermal and mechanical forces to which such distribution heads aresubjected.

Various other objects and advantages of the invention will become clearfrom the following description of an embodiment thereof, and the novelfeatures will be particularly pointed out in connection with theappended claims. Understanding of the invention will be facilitated byreferring to the accompanying drawings, in which:

FIG. l is a partial, cross sectional elevation of a uidized bed reactoraccording to the invention;

FIG. 2 is a detailed cross sectional view of one of the openings in thedistribution head of the invention; and

FIG. 3 is a partial cross sectional view of an alternative embodiment ofthe invention.

With reference to FIG. 1, the fluidized bed reactor, indicated generallyat 10, is composed of an upper main body portion 12 and a lower portion14, the two portions being joined together at 15. Depending on theparticular end use, insulation 17 may or may not be needed. Thedistribution head according to the invention is illustrated at 1S and isseen to be of a general conical shape. The reactor is also equipped withan inlet for solids 20 in the upper portion, a gas inlet 22 below thedistribution head, and a solids outlet 24 communicating directly withthe upper section 12 of the reactor. A close-titting sleeve 19 may beprovided for securing outlet 24 to head 18. Outlet 24 may, in someapplications, 'be located in the shell of upper section 12. The locationshown in FIGURE l is advantageous for the continuous withdrawal ofenlarged or heavier solid particles that settle in the bottom of thebed. Outlet 24 may, of course, be used to withdraw `normal particles aswell as lumps, or, alternatively, it

may be used to withdraw lumps only while normal particles are withdrawnthrough an outlet (not shown) located in the shell of upper section 12.

As can be seen from FIG. l, distribution head 1S is supported by acylindrical section 26 which is of a slightly smaller diameter than theinside diameter of the reactor shell 14. The cylindrical portion 26 isconnected at its upper extremity with annular plate 28 which is securedbetween the upper and lower sections of the reactor. It will beunderstood that this is an optional arrangement and other arrangementsfor fastening the distribution head within the reactor may be employed.It is only important that the vertical, cylindrical portion 26 be spacedfrom the inner wall of the reactor so as to allow forV thermal expansionand contraction of the conical portion 1-8. An expansion joint 30 isprovided in outlet 24 so that the conicalportion 18 is floating in allof its con nections to the reactor shell. For operation at elevatedtemperatures, heat llow to the metal shell is minimized by the use ofrefractory insulation 36 on the hot side of the distribution head and bythe tlow of cool gas on the underside.

By virtue of the generally conical shape of gas distribution head 13,there is provided a Very substantial resistance to any upward forcescaused by the gas pressure in lower section 14. Of even greaterimportance, distribution head 18 is designed so that the slope isgreater 'than the angle of natural repose of the particles, and thisprevents particles from building up or agglomerating thereon, whichwould interfere with proper gas flow and gas-solid contact. As is wellknown, for beds more than a few feet deep the downward force of asettled bed can be substantial, and the design of distribution head 18successfully withstands such pressures.

As is normal in lluidized beds designed for operation at elevatedtemperatures, refractory lining materials 17, 34 are provided in thereactor shell itself as noted above, and additional refractory 36 isprovided on the distribution plate to minimize heat llow to the metalparts.

The particular design of the apertures within the plate 1'8 isillustrated in FIGURE 2. With reference to this drawing, plate 18 isseen to be comprised of a conical steel plate 38 and the aforementionedrefractory material 36. Within the refractory material there is disposedan annular insert 40 having a substantially larger diameter at the upperend than at the lower end. This insert extends essentially through therefractory material but not through the steel plate 38. An insert 42 ofa porous material is provided, which is adapted to pass through theaperture in plate 38 and screw into or otherwise join with the insert40. As can be seen from FIG. 2, this insert or plug is closed at itslower end, but being porous provides little resistance to the upwardflow of gas therethrough. In the event of gas failure, however, thisplug will sustain the solid material within the reactor and prevent `thesame from passing through plate 1S and into the lower portion of thereactor. Of course, the embodiment illustrated in FIGURE 2 is not anecessary feature of the invention; perforations in the plate 38 andrefractory 36 are really all that is required (see FIGURE l).

An alternative embodiment of the invention, useful where two separatereactant gases must be introduced into the lluidized bed, is illustratedin FIGURE 3. In this embodiment, conduit 24 is utilized as a second gasinlet rather than as a solids outlet. As shown in the drawing, conduit24 extends'through distribution head 18 and well into upper section 12.It is capped at the top, and is provided with a plurality of radiallyextending arms 44, each of which is perforated. Gas flowing throughconduit 24 is thus evenly injected into the bed; mixing with the gaspassing through distribution head 18 is excellent, as those skilled inthe art will realize. The embodiment of FIGURE 3 is useful, for example,where two reactant gases are passed through a iluidized bed of catalystparticles.

Gas distribution heads for use in iluidized bed reactors employedheretofore have most commonly presented a 5 flat surface to theiluidizing portion of the reactor (except for the dome-shaped typesnoted hereinabove), it being felt Vthat this was necessary in order thata constant head be maintained above all portions of the distributionplate, thus insuring uniform fluidizing action and a proper upper,boiling surface free from large bubbles and the like. One of thesurprising aspects of the generally conical design of the distributionhead of the present invention is its effect on the fluidized bed.

For good gas distribution within the bed .the pressure to the pressuredrop through the holes. This effect requires very high gas velocitythrough the holes, which would in many instances be sufficient to causeattrition of solid particles. This ,is avoided, however, by the holeswith an expanding cross-section in the refractory. This reduces the jetvelocity and particle attrition s minimized.

It will be understood that various changes in the steps, details,materials and arrangements of parts, which have been hereinabovedescribed and illustrated in order to explain the nature of theinvention, may be made by those skilled in the art within the principleand scope of the invention as defined in the appended claims.

What is claimed is:

1. In a iluidized bed reactor comprising a reactor vessel, fluid inletmeans and outlet means, lthe improvements comprising:

a generally conical, perforated distributing grid ing a lowermostcentral' portion and a raised peripheral portion, said grid being abovesaid fluid inlet means and below said solid inlet means;

a cylindrical supporting portion secured in vapor tight connection atone end to said grid around the periphery thereof;

securing means at the other end of said supporting portion adapted toretain said supporting portion and grid in spaced relation to the wallsof said reactor vessel and in vapor tight connection between the portionof said vessel aboveand below said grid; and

second fluid inlet means below said grid, an aperture in the lowermostcentral portion of said grid, conduit means in communication with saidsecond fluid Y inlet means and passing through said aperture, and aplurality ofV radial gas-distributing conduits'in fluid communicationwith said conduit and extending therefrom over said grid. A.

2. Fluid distributing means for a fluidized bed reactor for .contactingfluids and a bed of solid particles, comprising:

a generally conical, perforated distributing grid having a low centralportion and a raised peripheral portion;

a conduit passing through an aperture in the vertex of said distributinggrid and having a plurality of radial fluid distributing conduits influid communication'L with said conduit and extending therefrom oversaid grid. e 3. The fluid distributing means as claimed in claim ,2'y

wherein said perforated distributing grid is for passing a rst fluidinto the bed of solid particles and said conduit is for passing a secondfluid into the bed of solid particles. 4. In a fluidized bed reactorhaving an upper main body portion and a lower main body portion, the im-7 provement comprising: a fluid distributing grid including; an uppercylindrical portion with an annular flange extending outwardlytherefrom; and a lower, generally conical, perforated portion;

said flange for positioning between said upper main s body portion andsaid lower main body portion to support the upper cylindrical portionand lower perforated portion of said distributing grid in lateral andvertical spaced relation to said lower main body portion.

5. The apparatus as claimed in claim 4 wherein said uid distributinggrid is a single element.

6. The apparatus as claimed in claim 4 wherein said lower main bodyportion is cylindrical and said upper cylindrical portion of saiddistributing grid is smaller in diameter than the inside diameter ofsaid lower main body portion.

7. The apparatus as claimed in claim 4 and further including:

an aperture in the vertex of said conical perforated portion of saiddistributing gn'd;

and a conduit in vapor tight engagement with said aperture for allowingescape of solid bed material from said fluidized bed.

8. The apparatus as claimed in claim 4 and further including:

an aperture in the vertex of said conical perforated portion of saiddistributing grid; and

a conduit in vapor tight engagement; with said aperture,

said conduit extending through and above said aperture, said conduit forthe introduction of a uid to the bed material of the bed reactor.

References Cited UNITED STATES PATENTS FREDERICK L. MATTESON, IR.,Primary Examiner.

20 I. I. CAMBY, Examiner.

